1. Field of the Invention
This invention relates to a solid-state electrolytic capacitor in which a capacitor element having an anode member with a dielectric film formed thereon is impregnated with conductive polymer serving as a cathode electrolyte and housed/sealed within an outer case.
2. Description of the Related Art
A previously known structure of a solid-state electrolytic capacitor is shown in FIG. 4, in which a capacitor element having an anode member with a dielectric film formed thereon is impregnated with conductive polymer serving as a cathode electrolyte and housed/sealed within an outer case.
In this solid-state electrolytic capacitor, a capacitor element 11 is manufactured in a manner that an anode foil with a dielectric film formed thereon and an opposite cathode foil are wound with a separator interposed therebetween. The capacitor element 11 is impregnated with conductive polymer serving as a cathode electrolyte. The capacitor element 11 is housed within a cylindrical bottomed outer case 15 and sealed by sealing rubber 16. A seat plate 18 for surface mounting is mounted on the sealed end of the outer case 15. In FIG. 4, reference numerals 17a and 17b denote terminals for extending the anode and the cathode, respectively.
Conventionally, in such a solid-state electrolytic capacitor, the following thing occurred. The conductive polymer impregnated in the capacitor element absorbs moisture during a manufacturing process after the conductive polymer has been formed. As a result, in a solder heat resistant test or endurance test executed for the completed product of the capacitor, the equivalent series resistance and the lead current increase.
JP-A-11-204377 discloses a technique that in such a solid-state electrolytic capacitor, in order to suppress gas generation from conductive polymer due to a solder heat resistance test, thereby preventing a case or sealing member from swelling, the outside of the capacitor element impregnated with conductive polymer is covered with epoxy resin.
However, the solid-state capacitor with an epoxy resin layer formed outside the capacitor element impregnated with conductive polymer according to the technique disclosed in JP-A-11-204377 has the following defect. Specifically, in the solder heat resistance test, as the case may be, mechanical stress is applied to the interior of the capacitor element owing to a difference in a thermal expansion coefficient between the members of the capacitor including conductive polymer and the epoxy resin layer so that the dielectric film on the anode member is damaged. As a result, the leakage current is increased very greatly.
An object of this invention is to provide a solid-state electrolytic capacitor including conductive polymer as a cathode electrolyte which is free from attenuation of the characteristic such as an increase in a leakage current.
In order to attain the above object, in accordance with the first aspect of this invention, there is provided a solid-state electrolytic capacitor in which a capacitor element having an anode member with a dielectric film formed thereon is impregnated with conductive polymer serving as a cathode electrolyte and housed/sealed within an outer case, wherein the capacitor element impregnated with conductive polymer is covered with epoxy resin mixed with a silane coupling element.
In accordance with this invention, after the conductive polymer has been formed, moisture absorption by this polymer is suppressed. Thus, during the solder heat resistant test and endurance test executed the product of the capacitor, the equivalent series resistance and leakage current are made difficult to vary.
In accordance with the second aspect of this invention, there is provided a solid-state electrolytic capacitor in which a capacitor element having an anode member with a dielectric film formed thereon is impregnated with conductive polymer serving as a cathode electrolyte and housed/sealed within an outer case, wherein the capacitor element impregnated with conductive polymer is covered with a first resin layer and a second resin layer which are formed successively on an outside thereof, and the first resin layer is made of a material having higher flexibility than that of the second resin layer.
In this configuration, since the capacitor element is covered with the first resin layer made of higher flexibility in intimate contact with the outside thereof, mechanical stress is difficult to spread to the interior of the capacitor so that the dielectric film within the capacitor element is difficult to be damaged.
Since the first resin layer is made of such a material, freedom of selecting the material of the second resin layer can be enhanced.
In this configuration of the solid-state electrolytic capacitor, it is possible to prevent the case or sealing member from being swelled during a solder heat resistance test, and to suppress an increase in the leakage current.
The above and other objects and features of this invention will be more apparent from the following description taken in conjunction with the accompanying drawings.